[semi-auto-props]: Refactor and rename 'AccessingAutoPropertyFromCons…

…tructor' (#58832)

src/Compilers/CSharp/Portable/Binder/Binder.ValueChecks.cs

@@ -1092,7 +1092,7 @@ private bool CheckPropertyValueKind(SyntaxNode node, BoundExpression expr, BindV
                 if (setMethod is null)
                 {
                     var containing = this.ContainingMemberOrLambda;
-                    if (!AccessingAutoPropertyFromConstructor(receiver, propertySymbol, containing)
+                    if (!IsPropertyAssignedThroughBackingField(receiver, propertySymbol, containing)
                         && !isAllowedDespiteReadonly(receiver))
                     {
                         Error(diagnostics, ErrorCode.ERR_AssgReadonlyProp, node, propertySymbol);

src/Compilers/CSharp/Portable/Binder/Binder_Statements.cs

@@ -1668,26 +1668,53 @@ private DiagnosticInfo GetBadEventUsageDiagnosticInfo(EventSymbol eventSymbol)
                 new CSDiagnosticInfo(ErrorCode.ERR_BadEventUsageNoField, leastOverridden);
         }
 
-        internal static bool AccessingAutoPropertyFromConstructor(BoundPropertyAccess propertyAccess, Symbol fromMember)
+        // PROTOTYPE(semi-auto-props): Re-evaluate if this helper is needed. There is one callsite only.
+        internal static bool IsEquivalentToBackingFieldRead(BoundPropertyAccess propertyAccess, Symbol fromMember)
         {
-            return AccessingAutoPropertyFromConstructor(propertyAccess.ReceiverOpt, propertyAccess.PropertySymbol, fromMember);
+            var propertySymbol = propertyAccess.PropertySymbol;
+            var receiver = propertyAccess.ReceiverOpt;
+            if (!propertySymbol.IsDefinition && propertySymbol.ContainingType.Equals(propertySymbol.ContainingType.OriginalDefinition, TypeCompareKind.IgnoreNullableModifiersForReferenceTypes))
+            {
+                propertySymbol = propertySymbol.OriginalDefinition;
+            }
+
+            return propertySymbol is SourcePropertySymbolBase sourceProperty &&
+                sourceProperty.GetMethod is SourcePropertyAccessorSymbol { IsEquivalentToBackingFieldAccess: true } &&
+                TypeSymbol.Equals(sourceProperty.ContainingType, fromMember.ContainingType, TypeCompareKind.ConsiderEverything2) &&
+                    IsConstructorOrField(fromMember, isStatic: sourceProperty.IsStatic) &&
+                    (sourceProperty.IsStatic || receiver.Kind == BoundKind.ThisReference);
+        }
+
+        internal static bool IsPropertyAssignedThroughBackingField(BoundPropertyAccess propertyAccess, Symbol fromMember)
+        {
+            return IsPropertyAssignedThroughBackingField(propertyAccess.ReceiverOpt, propertyAccess.PropertySymbol, fromMember);
         }
 
-        private static bool AccessingAutoPropertyFromConstructor(BoundExpression receiver, PropertySymbol propertySymbol, Symbol fromMember)
+        /// <summary>
+        /// Determines whether a property is assigned through the backing field within a symbol <paramref name="fromMember"/>
+        /// </summary>
+        /// <remarks>
+        /// A property is assigned through backing field within a constructor or a field initializer.
+        /// </remarks>
+        private static bool IsPropertyAssignedThroughBackingField(BoundExpression receiver, PropertySymbol propertySymbol, Symbol fromMember)
         {
             if (!propertySymbol.IsDefinition && propertySymbol.ContainingType.Equals(propertySymbol.ContainingType.OriginalDefinition, TypeCompareKind.IgnoreNullableModifiersForReferenceTypes))
             {
                 propertySymbol = propertySymbol.OriginalDefinition;
             }
 
-            var sourceProperty = propertySymbol as SourcePropertySymbolBase;
-            var propertyIsStatic = propertySymbol.IsStatic;
+            // PROTOTYPE(semi-auto-props): TODO: Support assigning semi auto prop from constructors.
 
-            return (object)sourceProperty != null &&
-                    sourceProperty.IsAutoPropertyWithGetAccessor &&
+            return propertySymbol is SourcePropertySymbolBase sourceProperty &&
+                    // PROTOTYPE(semi-auto-props): Consider `public int P { get => field; set; }`
+                    sourceProperty.GetMethod is SourcePropertyAccessorSymbol { IsEquivalentToBackingFieldAccess: true } &&
+                    // To be assigned through backing field, either SetMethod is null, or it's equivalent to backing field write
+                    // PROTOTYPE(semi-auto-props): TODO: Do we need to use `GetOwnOrInheritedSetMethod` instead of `SetMethod`?
+                    // Legacy auto-properties are required to override all accessors. If this is not the case with semi auto props, we may need to use GetOwnOrInheritedSetMethod
+                    sourceProperty.SetMethod is null or SourcePropertyAccessorSymbol { IsEquivalentToBackingFieldAccess: true } &&
                     TypeSymbol.Equals(sourceProperty.ContainingType, fromMember.ContainingType, TypeCompareKind.ConsiderEverything2) &&
-                    IsConstructorOrField(fromMember, isStatic: propertyIsStatic) &&
-                    (propertyIsStatic || receiver.Kind == BoundKind.ThisReference);
+                    IsConstructorOrField(fromMember, isStatic: sourceProperty.IsStatic) &&
+                    (sourceProperty.IsStatic || receiver.Kind == BoundKind.ThisReference);
         }
 
         private static bool IsConstructorOrField(Symbol member, bool isStatic)

src/Compilers/CSharp/Portable/FlowAnalysis/AbstractFlowPass.cs

@@ -571,7 +571,7 @@ protected void VisitLvalue(BoundExpression node)
                 case BoundKind.PropertyAccess:
                     var access = (BoundPropertyAccess)node;
 
-                    if (Binder.AccessingAutoPropertyFromConstructor(access, _symbol))
+                    if (Binder.IsPropertyAssignedThroughBackingField(access, _symbol))
                     {
                         var backingField = (access.PropertySymbol as SourcePropertySymbolBase)?.BackingField;
                         if (backingField != null)
@@ -1915,7 +1915,7 @@ private bool RegularPropertyAccess(BoundExpression expr) // PROTOTYPE(semi-auto-
                 return false;
             }
 
-            return !Binder.AccessingAutoPropertyFromConstructor((BoundPropertyAccess)expr, _symbol);
+            return !Binder.IsPropertyAssignedThroughBackingField((BoundPropertyAccess)expr, _symbol); // PROTOTYPE(semi-auto-props): Revise this method call is the behavior we want and add unit tests..
         }
 
         public override BoundNode VisitAssignmentOperator(BoundAssignmentOperator node)
@@ -2051,7 +2051,9 @@ public override BoundNode VisitPropertyAccess(BoundPropertyAccess node)
         {
             var property = node.PropertySymbol;
 
-            if (Binder.AccessingAutoPropertyFromConstructor(node, _symbol))
+            // PROTOTYPE(semi-auto-props): Add tests for semi auto property once assigning in constructors is supported.
+            // A test that gets to this code path can be similar to CodeGenConstructorInitTests.TestInitializerInCtor003
+            if (Binder.IsEquivalentToBackingFieldRead(node, _symbol))
             {
                 var backingField = (property as SourcePropertySymbolBase)?.BackingField;
                 if (backingField != null)

src/Compilers/CSharp/Portable/FlowAnalysis/DefiniteAssignment.cs

@@ -964,7 +964,10 @@ protected override bool TryGetReceiverAndMember(BoundExpression expr, out BoundE
                     {
                         var propAccess = (BoundPropertyAccess)expr;
 
-                        if (Binder.AccessingAutoPropertyFromConstructor(propAccess, this.CurrentSymbol))
+                        // PROTOTYPE(semi-auto-props): The call to IsPropertyAssignedThroughBackingField isn't sensible.
+                        // We get here for both property read and write.
+                        // This applies to ALL IsPropertyAssignedThroughBackingField calls in this file.
+                        if (Binder.IsPropertyAssignedThroughBackingField(propAccess, this.CurrentSymbol)) // PROTOTYPE(semi-auto-props): Revise this method call is the behavior we want and add unit tests..
                         {
                             var propSymbol = propAccess.PropertySymbol;
                             member = (propSymbol as SourcePropertySymbolBase)?.BackingField;
@@ -1189,7 +1192,7 @@ private bool IsAssigned(BoundExpression node, out int unassignedSlot)
                 case BoundKind.PropertyAccess:
                     {
                         var propertyAccess = (BoundPropertyAccess)node;
-                        if (Binder.AccessingAutoPropertyFromConstructor(propertyAccess, this.CurrentSymbol))
+                        if (Binder.IsPropertyAssignedThroughBackingField(propertyAccess, this.CurrentSymbol)) // PROTOTYPE(semi-auto-props): Revise this method call is the behavior we want and add unit tests..
                         {
                             var property = propertyAccess.PropertySymbol;
                             var backingField = (property as SourcePropertySymbolBase)?.BackingField;
@@ -2240,7 +2243,7 @@ public override BoundNode VisitFieldAccess(BoundFieldAccess node)
         public override BoundNode VisitPropertyAccess(BoundPropertyAccess node)
         {
             var result = base.VisitPropertyAccess(node);
-            if (Binder.AccessingAutoPropertyFromConstructor(node, this.CurrentSymbol))
+            if (Binder.IsPropertyAssignedThroughBackingField(node, this.CurrentSymbol)) // PROTOTYPE(semi-auto-props): Revise this method call is the behavior we want and add unit tests..
             {
                 var property = node.PropertySymbol;
                 var backingField = (property as SourcePropertySymbolBase)?.BackingField;

src/Compilers/CSharp/Portable/Symbols/Source/SourcePropertyAccessorSymbol.cs

@@ -466,6 +466,11 @@ internal Accessibility LocalAccessibility
         /// </summary>
         internal bool BodyShouldBeSynthesized => _bodyShouldBeSynthesized;
 
+        /// <summary>
+        /// Indicates whether this get/set accessor is equivalent to a backing field read/write.
+        /// </summary>
+        internal bool IsEquivalentToBackingFieldAccess => _bodyShouldBeSynthesized;
+
         /// <summary>
         /// Indicates whether this accessor is readonly due to reasons scoped to itself and its containing property.
         /// </summary>

src/Compilers/CSharp/Test/Semantic/FlowAnalysis/RegionAnalysisTests.cs

@@ -145,6 +145,144 @@ static void Main(string[] args)
             Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.CapturedOutside));
         }
 
+        [Fact]
+        public void DataFlowsInAndNullable_Property_InConstructor()
+        {
+            var dataFlowAnalysisResults = CompileAndAnalyzeDataFlowStatements(@"
+struct S
+{
+    public int F;
+    public S(int f)
+    {
+        this.F = f;
+
+        int? i = 1;
+        S s = new S(1);
+
+/*<bind>*/
+        Console.WriteLine(i.Value);
+        Console.WriteLine(s.P);
+/*</bind>*/
+    }
+
+    public int P { get; set; }
+}
+");
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.VariablesDeclared));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.AlwaysAssigned));
+            Assert.Equal("i, s", GetSymbolNamesJoined(dataFlowAnalysisResults.DataFlowsIn));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.DataFlowsOut));
+            Assert.Equal("f, i, s", GetSymbolNamesJoined(dataFlowAnalysisResults.DefinitelyAssignedOnEntry));
+            Assert.Equal("f, i, s", GetSymbolNamesJoined(dataFlowAnalysisResults.DefinitelyAssignedOnExit));
+            Assert.Equal("i, s", GetSymbolNamesJoined(dataFlowAnalysisResults.ReadInside));
+            Assert.Equal("this, f", GetSymbolNamesJoined(dataFlowAnalysisResults.ReadOutside));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.WrittenInside));
+            Assert.Equal("this, f, i, s", GetSymbolNamesJoined(dataFlowAnalysisResults.WrittenOutside));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.Captured));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.CapturedInside));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.CapturedOutside));
+        }
+
+        [Theory]
+        [InlineData("get;", true)]
+        [InlineData("get; set;", true)]
+        [InlineData("get => 0;", false)]
+        [InlineData("get => 0; set => _ = value;", false)]
+        public void DataFlowsInAndNullable_InstanceProperty(string accessors, bool isAutoProp)
+        {
+            var dataFlowAnalysisResults = CompileAndAnalyzeDataFlowStatements($@"
+struct S
+{{
+    public int P {{ {accessors} }}
+
+    public S(int p)
+    {{
+        this.P = p;
+    }}
+
+    static void Main(string[] args)
+    {{
+        S s = new S(1);
+
+/*<bind>*/
+        Console.WriteLine(s.P);
+/*</bind>*/
+    }}
+}}
+");
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.VariablesDeclared));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.AlwaysAssigned));
+            Assert.Equal("s", GetSymbolNamesJoined(dataFlowAnalysisResults.DataFlowsIn));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.DataFlowsOut));
+            Assert.Equal("args, s", GetSymbolNamesJoined(dataFlowAnalysisResults.DefinitelyAssignedOnEntry));
+            Assert.Equal("args, s", GetSymbolNamesJoined(dataFlowAnalysisResults.DefinitelyAssignedOnExit));
+            Assert.Equal("s", GetSymbolNamesJoined(dataFlowAnalysisResults.ReadInside));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.ReadOutside));
+
+            if (isAutoProp)
+            {
+                Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.WrittenInside));
+            }
+            else
+            {
+                Assert.Equal("s", GetSymbolNamesJoined(dataFlowAnalysisResults.WrittenInside));
+            }
+
+            Assert.Equal("args, s", GetSymbolNamesJoined(dataFlowAnalysisResults.WrittenOutside));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.Captured));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.CapturedInside));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.CapturedOutside));
+        }
+
+        [Theory]
+        [InlineData("get;", true)]
+        [InlineData("get; set;", true)]
+        [InlineData("get => 0;", false)]
+        [InlineData("get => 0; set => _ = value;", false)]
+        public void DataFlowsInAndNullable_InstanceProperty_InConstructor(string accessors, bool isAutoProp)
+        {
+            var dataFlowAnalysisResults = CompileAndAnalyzeDataFlowStatements($@"
+struct S
+{{
+    public int P {{ {accessors} }}
+
+    public S(int p)
+    {{
+        this.P = p;
+
+        S s = new S(1);
+
+/*<bind>*/
+        Console.WriteLine(s.P);
+/*</bind>*/
+    }}
+}}
+");
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.VariablesDeclared));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.AlwaysAssigned));
+            Assert.Equal("s", GetSymbolNamesJoined(dataFlowAnalysisResults.DataFlowsIn));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.DataFlowsOut));
+            Assert.Equal("this, p, s", GetSymbolNamesJoined(dataFlowAnalysisResults.DefinitelyAssignedOnEntry));
+            Assert.Equal("this, p, s", GetSymbolNamesJoined(dataFlowAnalysisResults.DefinitelyAssignedOnExit));
+            Assert.Equal("s", GetSymbolNamesJoined(dataFlowAnalysisResults.ReadInside));
+            Assert.Equal("this, p", GetSymbolNamesJoined(dataFlowAnalysisResults.ReadOutside));
+
+            if (isAutoProp)
+            {
+                Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.WrittenInside));
+                Assert.Equal("p, s", GetSymbolNamesJoined(dataFlowAnalysisResults.WrittenOutside));
+            }
+            else
+            {
+                Assert.Equal("s", GetSymbolNamesJoined(dataFlowAnalysisResults.WrittenInside));
+                Assert.Equal("this, p, s", GetSymbolNamesJoined(dataFlowAnalysisResults.WrittenOutside));
+            }
+
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.Captured));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.CapturedInside));
+            Assert.Null(GetSymbolNamesJoined(dataFlowAnalysisResults.CapturedOutside));
+        }
+
         [WorkItem(538238, "http://vstfdevdiv:8080/DevDiv2/DevDiv/_workitems/edit/538238")]
         [Fact]
         public void TestDataFlowsIn03()